FOSSILS. 597 



on each side of the mesial fold and sinus, strong, and much elevated, 

 subangular, crossed by numerous strongly elevated, lamellose, imbri- 

 cating concentric strife. 



The specimens examined are almost all imperfect casts, some of 

 which preserve the impression of the strong concentric strise, and in 

 one or two specimens an impression of the shell reveals the strength 

 of the surface markings. 



In many respects this species resembles the S. perlamellosa of the 

 Lower Helderberg group in New York, but the mesial elevation of this 

 species is flattened or depressed, a character never observed in New 

 York specimens. Arisaig, East River, coll. J. W. D. 



Spu^ifer subsulcatus, Hall. Shell semi-elliptical, hinge-line equalling 

 or greater than the length of the shell below ; plications five or six 

 on each side of the mesial fold ; mesial fold somewhat flattened or 

 very slightly rounded on the summit ; plications rounded ; surface 

 concentrically lamellose. 



Tlie specimens are all casts, or impressions of the shells. 



They bear some resemblance to S. sulcatus of the Niagara group, 

 and are intermediate between that species and the S. cycloptera of the 

 Lower Helderberg group. Arisaig, East River, coll. J. W. D. 



Spirifera, resembling >S. cyclop)tera^ but with regular ribs. East 

 River, coll. J. W. D. 



Strophomena profunda^ Hall. Arisaig, coll. J. W. D. Dalhousie, 

 Professor Bailey. 



S. rugosa. Arisaig. 



S. flat sti-iated species. East River, coll. J. W. D. 



S. corrugata, Conrad. Arisaig, coll. J. W. D. 



Tremastospira Acadice, Hall (Fig. 201). Shell wider than long; 

 beak of the ventral valve produced and incurved ; mesial depression 

 marked by a small fold on each side, which originates about one-third 

 of the length below the beak and continues to the margin ; sinus 

 bounded on each side by a more strongly elevated plication, beyond 

 which are six other plications on each side. Surface marked by fine 

 concentric striaj. 



This shell is referred to the genus Trcmatospira from external 

 characters alone, which arc unlike Rhynchonella propei', and the shell 

 is not a Spirifer. Arisaig, coll. J. W. D. 



Rhjnchospira slnuata, n. sp. Shell ovoid, ventricose beak of the 

 ventral valve incurved; a mesial sinus beginning a little below the 

 beak ; surface marked by about eight or nine simple scarcely sub- 

 angular plications on each side of the mesial sinus. 



Surface marked by concentric lines of growth. 



